"He had a scan two days ago and he's out for a while", Wenger told reporters.
Sanchez's future remains uncertain with his contract up next season and Manchester City determined to sign him.
"He had a little abdominal strain that he caught on Sunday morning in training, before he came to Wembley (for the FA Community Shield final on Sunday)", Wenger was quoted as saying by Arsenal's website on Tuesday. "I can take a gamble on one, maybe maximum two", Wenger said.
The Gunners boss said in a press conference that the Chilean worldwide has an abdominal strain and could be out for one or two weeks.
However, Wenger seemed convinced that Sanchez - who is in the previous year of his contract - will be going nowhere this summer. "But all the other players prepared in preseason and are ready", Wenger said. I remember watching him at Bournemouth last season and he looked angry.
Obviously it will be a huge blow to be without Sanchez for the start of the season but we have even greater concerns to worry about in defence as Per Mertesacker is also a major doubt for Friday's clash.
"It's a long time since I spoke with Nasser because he was certainly very busy to complete the transfer of Neymar", Wenger said.
But he is no closer to shifting those deemed surplus to requirements as he believes many Premier League clubs are in the same position.